Fair Value Measurements (Tables)
3 Months Ended
Mar. 31, 2015
Fair Value Disclosures [Abstract]  
Fair Value, Assets Measured on Recurring and Nonrecurring Basis
The following tables provides a summary of financial assets that are measured at fair value on a recurring basis as of March 31, 2015 and December 31, 2014, aggregated by the level in the fair value hierarchy within which those measurements fall (in thousands):
 
Fair Value Measurements
 
Total
 
Level 1
 
Level 2
 
Level 3
March 31, 2015
 
 
 
 
 
 
 
   Cash Equivalents - Money Market Funds
$
123,155

 
$
123,155

 
$

 
$

December 31, 2014
 
 
 
 
 
 
 
   Cash Equivalents - Money Market Funds
$
123,141

 
$
123,141

 
$

 
$

Fair Value, Liabilities Measured on Recurring and Nonrecurring Basis
The carrying amounts and the estimated fair values of financial instruments as of March 31, 2015 and December 31, 2014, are as follows (in thousands):
 
March 31, 2015
 
December 31, 2014
 
Carrying
Value
 
Estimated Fair
Value
 
Carrying
Value
 
Estimated Fair
Value
2% Convertible Senior Notes
$
170,595

 
$
202,377

 
$
168,994

 
$
237,475